On my windows 8.1 running Windows Defender as default antivirus. Not faced with similar problems.
What your OS? Windows Defender is updated? OS is updated?
I recommend periodically checking system of good antivirus software: Kaspersky or Dr.Web. Miscellaneous Trojans and malicious plugins good catch: Malwarebytes and SUPERAntiSpyware.
Windows 10 Insider Preview, x64